Conventional switched reluctance machines feature a rugged structure, robust performance in harsh ambient conditions, and low manufacturing cost. However, the majority of the electromagnetic forces generated by a conventional switched reluctance machine does not contribute to useful work, and a significant proportion of these forces generates undesirable vibrations that have been identified as a major drawback for such machines. Thus, limited torque density and energy conversion efficiency, among other characteristics, of conventional switched reluctance machines has limited their industrial applicability.
For example, U.S. Pat. No. 5,304,882 to Lipo et al. discloses a variable reluctance motor with permanent magnet excitation having a single set of stators and a single rotor having permanent magnets. However, the motor in Lipo requires a significant amount of permanent magnet material, thereby making the manufacturing of such motor expensive. Further, the disclosed motor is limited in the amount of electromagnetic forces contributing to rotational motion, thereby limiting the torque density of the motor and the overall efficiency of the motor.
Therefore, there is a need in the art for a switched reluctance machine in which a higher proportion of the electromagnetic forces generated contributes to motion with a reduced amount of permanent magnet material, thereby lowering the overall cost of manufacturing.